This invention relates to high efficiency lighting sources.
The era of the Edison vacuum light bulb may soon end. In many countries, and in many states, incandescent bulbs are being replaced, and more efficient lighting sources mandated. Alternative light sources include fluorescent tubes, halogen, and light emitting diodes (LEDs). Despite the availability and improved efficiencies of these options, many people are reluctant to switch to these alternative light sources.
The newer technologies have not been widely embraced for various reasons. One such reason is the use of toxic substances in the lighting source. As an example, fluorescent lighting sources typically rely upon mercury in a vapor form to produce light. Because the mercury vapor is a hazardous material, spent lamps cannot simply be disposed of at the curbside, but must be transported to designated hazardous waste disposal sites. Additionally, some fluorescent tube manufacturers instruct the consumer to avoid using the bulb in sensitive areas of the house such as bedrooms.
Another reason for the slow adoption of alternative lighting sources is its low performance compared to the incandescent light bulb. Fluorescent lights rely upon a separate starter or ballast mechanism to initiate the illumination. Thus they sometimes do not turn on “instantaneously” as consumers expect. In addition fluorescent lights typically do not immediately provide light at full brightness, instead ramping up to full brightness over time. Further, most fluorescent lights are fragile, are not capable of dimming, have ballast transformers that can be noisy, and can fail if cycled on and off frequently.
Another type of alternative lighting source more recently introduced relies on the use of light emitting diodes (LEDs). LEDs have advantages over fluorescent lights including the robustness and reliability inherent in solid state devices, the lack of toxic chemicals that can be released during accidental breakage or disposal, instant-on capabilities, dimmability, and the lack of audible noise. LED lighting sources, however, have drawbacks that cause consumers to be reluctant to use them.
One disadvantage with LED lighting is that the light output (e.g. lumens) is relatively low. Although current LED lighting sources draw a significantly lower amount of power than their incandescent equivalents (e.g. 5-10 watts v. 50 watts), they can be too dim to be used as primary lighting sources. For example, a typical 5 watt LED lamp in the MR16 form factor may provide 200-300 lumens, whereas a typical 50 watt incandescent bulb in the same form factor may provide 700-1000 lumens. As a result, current LEDs are often used only for accent lighting or in areas where more illumination is not required.
Another drawback of LED lighting is the upfront cost of the LED. A current 30 watt equivalent LED bulb costs over $60, in comparison to an incandescent floodlight costing about $12. Although the consumer may “make up the difference” over the lifetime of the LED in reduced electricity costs, the higher initial cost suppresses demand.
Another concern with LED lighting is the amount of parts and the labor of production. An MR16 LED light source from one manufacturer requires 14 components, while another utilizes more than 60 components. Another disadvantage of LED lighting is that the output performance is limited by the need for a heat sink. In many applications, the LEDs are placed in an enclosure with poor air circulation, such as a recessed ceiling enclosure, where the temperature is usually over 50 degrees C. At such temperatures the emissivity of surfaces play only a small roll in dissipating heat. Further, because conventional electronic assembly techniques and LED reliability factors limit PCB board temperatures to about 85 degrees C., the power output of the LEDs is also constrained. Traditionally, light output from LED lighting sources have been increased by simply increasing the number of LEDs, which has lead to increased device costs, and increased device size. Additionally, such lights have had limited beam angles and limited outputs.